Treatment of fresh fruits and vegetables for decay control



Patented July 22, 1952 J arm-cs TREATMENT OF FRESH JFRUI'ISNAND VEGETABLESirFOR DECAY CONTROL CharlesD." Cothran; Pomona, Califl, assig or, by

mesne assignments, to Brqgfiex- Company; Pomona Calif.; ar'corporation= I No Drawing; Application J une115, 1946,.

. Serial N 0. 677,103.-

181 Claims; (Cl; 9 9156)-- particularly when not--protective1ytreated inf some way, are commonly" subject while-being shipped to marketing centers and distributed to ultimate consumers. Reference herein to fresh fruits and-vegetablesisto be understood as conforming-with common usage-in the commodity shippingand:- marketing industry, such designation being confined-to whole fruits andvege tables supplied to consumers substantially. as

harvested, not peeled or s1iced.- I

It has long been recognized that it isessential to take special preventive measures, in"; commercially preparing fruit and vegetables for shipment to market and distribution to consumers, if. serious losses from decay are to-be avoided. Most such decay is causedby fungoid types of decay or rot organisms, of which-the well known blue: and green penicillium.molds so often seen on citrus fruits especiallyare amongv the more: common. Another example is stem-end rot, which'causes' much spoilage in shipments of Florida oranges and grapefruit: Lemons are often attacked by penicillium molds, as well as by other types of fungus'rotsiso also are cantaloupes, tomatoes and other fruits and vegetables.

Ever since the now' well known borax'treatment' for decay prevention (patent of Brogden and Trowbridge 1,529,461) became availableto the industry, fresh fruit packers and shippers have hadat hand achemical method of cutting down. decay losses'with remarkable efi'ectiveness in the case of blue and greenmold rots; and with asubst'antial though lower degree of ef fectiveness in the case of stem-end rotalsoz Widespread adoption of the borax treatment followed immediately upon its introduction. in 1923, to such an extent that, for approximately the last twenty years, use of thismethod has been virtually universal standard practice in fresh citrus fruit packing houses especially. The action of the borax in this treating method ap- 2". pears to be-inhibitory" rather than: actively fum gicidal. I

Notwithstanding the remarka'ble effectiveness of": the" b'orax treatment. the-sea1+ch for com mercially useful 'decay control agents has neventheless gone on almost"uninterruptedly through out the: long-period 'aforesjaidyp'artlyin -the hope of discovering one-that -wouldprove even more elfective than borax" againstthe penicillium type of. rots, and also" in-particular, onemote effective: than boraxin controlling steme'end rot: but th'esearch hasbeen'largely 'devoid of results having important practical utility for ti le -industry. The extreme sensitiveness of fresh fruits and many fresh vegetables to skin or rind injury that will adversely affect their appearance, and hence their marketability, sharply restricts the choice of a suitable decay control agentr Within recent years, it was found that application of a.. water solution of thiourea to Florida oranges afforded them substantial protection: against stem-end rot as well as blue and green molds, without injuring the rind of the fruit. Commercial utilization of this discovery has notbeenfeasible, however, due to the objectionable physiological effect of thiourea on the thyroid gland, and to the fact that, in the knownmethods of application, the residue left on the treatedoranges is officially regarded as being great enough to constitute, for this reason, a hazard to the health of consumers.

Believing that the presence in the thiourea molecule of sulphur in association with two amino groups might perhaps account for the effectiveness of thiourea as a decay-control agent, this applicant set about trying to find, among the large number of organic compounds known to be chemically constituted in a broadly analogous manner, some one or more that would be equally or sufiiciently effective for decay control but having no, or at least less, objectionable treated therewith. But it was eventually discovered that thioacetamide, as well as other water-soluble amides of thioacids of the fattty acid series, are highly effective and practical to employ in preventing or controlling fruit and vegetable rots of the kinds above mentioned.

tables in preparation for market should therefore be unobjectionable.

Tables A and B given below show the results of a number of tests, in each of which a portion of a given lot of fruit, infected with a fruit rot, was treated with a water solution of thioacetamide, a second portion was treated with a thiog 4 puncturing the rind in several places or cutting small pieces out of it, dipping the fruits in a water suspension of the spores of the penicillium molds, or painting such suspension on the wounds, and then holding the inoculated fruits, for 18110 24 hours under conditions favorable to starting incubationfof thelrot organisms e. g. at about 70 F. and 85 per cent relative humidity.

The remaining procedure was the same in both Table A and Table B tests. That is, all the infected fruits were washed in water at 110 F. for three minutes, and allowed to drain. Different groups or portions, each consisting of a known number (e. g. 25 or more) of the infected fruits, were treated by dipping in water solutions of thioacetamide and thiourea, respecurea solution, and a third portion was left untreated and served as control checks. In most of the tests, the concentration of one or both of the control agents was varied. In each test, the conditions to which the several portions or groups :of vfruits were subjected were the same except asto the decaycontrol agent used. In the Table "A tests, the fruit used-was artificially inoculated with blue and" green penicillium molds; while in the Table 3 tests, fruit wasused which was known to be already naturally infected with both stem-end rot and. green. mold.. The general procedure followed in preparing the fruit used joculate all specimens of a given test lot by either 30 in the Table A tests was first to artificially indecay had developed, and hence the percentage decay in each group at the dated each inspection.

Table A.C'aliform'a lemons and oranges artificially inoculated with penicilhum molds Fruit Treated Percentage of fruits showing decay after number of days indicated Treatment 1 Lemons Lemons Lemons Lemons l\lavel Oranges.

Navel Oranges Navel Oran ges Navel Oranges None (checks)- L 5% Thioureaflnr .0 5% Thioacetamide. {None (checks) 5% Thiourea 5% Thioacctamide. 3.5% Thioacetamide" 2% Thioacetamide 1% Thioacetamid 0.5% Thioacetamide {None (checks) 5% Thiourea 2.5% Thiourea 5% Thioacetamiden" 2.5% Thioacetamide...

None (checks) 1% Thiourea 5% Thioacetamide. 2.5% Thioacetamide...

1% Thioacetamide..

3% Thioac 2% Thioacetamidm 1% Thioacetamide l L- r I i 5% Thicurea. 2.5% Thiourea 5% Thioacetamide. 2.5% Thioacetamide None (checks) 5% Thiourea 2.5% Thiourea. 0. 1.0% Thiourea 5% Thioacetamide 2.5% Thi0acetamide 1% Thioacetamide None (checks).

omoowootooooomccoooooooooopomo p.

5% Thioacetarnidm": 2.5% Thioacetamidem 1% Thioacetamide.

emu ems f5 6v Table B;.-.-Elorz'da: oranges; naturally injected-i.

withz-bothrstem-end SE); andzgreen moldi.(GM") V 1 Percentagedof 'decag'atgegznumber' Treatment I o ays m 108 e Noneichccks); V I SE I 1.3. l2.7 22:3: 33:8 ll-41 GM 1.3 2.3 2.31 3.5,. 3.5 None (checks)' SE 1.3 14. 19. 8 27. 9 I 34.-9-'

. GM 1.3 2.3 a e-5 as. 3. 5: 4%Thiourea SE 0 0 '0'." I r 0 v GIVI- 0 ;.O: L.

2%"Ihiourea SR 0 0 o 0 V 6. a

' GM 0 I 0 '0 o 1..4 1%Thiourea SE 0 0 5. 6"- 11. 1 20.8 1 I I GM, 0 1.4 la'i 1 2.8} 1 2.18" 4%"Thioacetamide (Source X) '.I. I SE1 0 0 114' "$1.4" 2Z8 GM '0 0' 1:41 1.4 228 2%;Thl08-(3Qtfl1flid9.(SODICO X) 5E5 ,0 0 9:7 19.41 30.6: GM 0 0 0 0 0 v I I 7 1o 14 1s 21 24 28 "None(c11eck5) sE: 0 o 10.3 19:11:: -=.3o;'9r' 41.2: 50:0: GM. 1.5 2.9v 2.9 14.4. 4.4. 4.4. .4.-.4-. None(checks); -4 SE 0 I 3.3 6.6 11:6 "2323' 36:6 4510 GMLI 1.6 1.6 1.6 .3113: 313:. 5.0 r' 5.0: 4% Ihiourea .SE 0 0 1.4 1.4. 1.4 1.1.4 1.4.

'GM 0 0 o 0*0 o .0" 2% Thiourca SE 0" 0 O 0; 0:. 0 0i GM 1.4 1.4 1.4 21; ".211 I 2.9.. 2.9. 2 1% Thiourea SE 0 0 0 -0 14' 219' 15.9-

' GM 0 0 0 L0: o 0130' 4% ThiQacetamide (Sourcc.X). I SE 0 0 0 0 1.5. 1.5 7 GM 0 0 0 o o o 0' 4% Thioacetamide(Sourcc'Y) SE 0 O 0 g 0* O O1 2.9

I GM: I 0 0 0,v 1.4 1.4. 14 1.4 2% Thioacetamide (Source'X).. SE 0 0 1.4 42-3' 11.6 17:4 2417' GM"'(). 0 0 =01 o- .o:= o 2% Thioacetamide:(Source Y) I SE. 0. 0 0. 0. 0 7.1.v l0-0 GM I o I o 0 o o I 2:9 22a Fromithe,foregoingdatait willbels'een that for figures; hereinabove given. for effectiveness of controlling decay-of lemonsvin-fectedwith penicilcontrol of. stem-end rot, as well aspenicillium lium molds; thioa'cetan -iideisr notablymore; effec rots,-by'thioacetamide are-properly-to'be regarded tive-than thiourea; and that iorcontrollingdecay as. conseevative. The indications are that: thicof similarly infected'navel o1anges,;thioacetamide acetami de: is quite. as: effeotivegas thioureaegor issomewhat moreefiective thanthiourea in. 51% perhaps even more effective,incontrollingjsteme water'solution; and somewhatless-effective than endrot.- Y Y thiourea at 2.5%; while at 1'% concentration;v the Where, the-thioacetamide is of, relatively high effectiveness of bothagents is relativelylowand purity, use of itat ordinaryroomitemp'erature roughly equal.-'. .(e. g. 70 F) in Water solution, at asrlowa con.-

As regards stem-end rot; a- 4% thioacetamide centratlon as 11% gives control of decay from solution iskshown by the: data in TableBto; give both. stem-end? ancl=penicillium rotorganisms to substantially 100% control, or. somewhat better a degree that'is commercially very'important. than a thiourea-solution; overra. holdingpet- Concentrations.-substantiallyloWer:-than 1% have 'riod-of' two weeks; at the. endof' which the: decay not been found sufficiently effective toxbe desir-' fromstem-end.rotzinatheuntreatedchecksiaver= 5O ableforcommerciaLnse; ifthetreating'solution aged more than.10%... At theaend of three'weeks, isapplied. inunheat'edpondition. 'Withunheated when decay from.stem-endrot'averaged '3'3.%'in solutions andreasonably' brief time: of contact the. checks, the: control by"4 %-,thioacetamide Withthe treatingsolutionat'its'original c.oncen-.- solution averagedi 95% as against 97;5.%- by 4:.% tration, maximum. efficiency in decay control thiourea solution. At the end of four weeks, with seems to be attained at concentrations. inthe 4.? stem-end decay. in the. checks,zthe:efiec.tiveneighborhood of. 41 to. 5 percenttv In practice, ness of'controliby-these4%?solutionswasrnearly therefore, use of treating solutions; containing 94 for-thioacetamide and:9.7% for thiourea; At thioacetamidesa't' concentrations .withinthisaplower concentrations, however,- sorfarras can be proximate range: is: regardediasmost desirable; inferred fromthese-particular-tests,theeflfectivevon Much stronger solutions, e; g. 10 to l-Bper: cent, ness of thioaceta'mide-in control ling stem-end canbe used without causingfim'ury tothefruit rot'falls; oil" faster than does thatv of thiourea. or vegetable treatedybut-as the decayrcontrolling Nevertheless, it appears that control by ar2% action of thioacetamide appears not to increase thioacetamide' solution is 100%' effective for-1O appreciably, norrto become-more-dependablebee to IZ-days; and averages 62% at the: end of 18 (i5 yond aconcentration of about:'5percent,.em-.- days, 49% at the-end of .21 days;and:41% at the ployment of stronger solutions ordinarily afiords end of 28 days; I r no practical advantaget It has been found that thioacetamide, as com- By applying a thioacetamide treating-gsoluti'on mercia-lly available; sometimes contains impuriof given concentration at. temperatures; higher tieswhich adversely afieotits action as aadecay the-n70 F; its eliectiveness 'incontrolling decay; controlagent, and reduce itselfectiveness maif below maximum at.70?; canbe: materially 'interiallyrto such an extent that comparative decreased. As thioacetamideiin:water'solution does cay control testsemploying lots 'obtainedfrom not decomposebelow ab0ut'1-58?'F;,.it is feasible different sourcessometirnes giveerratic or con-.- in practicing theinventionto-applyv a? treating flicting; results; Accordingly the. percentage solution; thereof, at anyttemperaturexup. to the By using this or any other explanation or theory of the r effectiveness of the herein disclosed process.

same time get equally good effective decay 'control. This also enables the use of lower concentrations than would be at all practicable commercially to employ at 70 F; 'But where the higher temperature used requires heating the solution artificially, the increased cost may more than offset the saving in amount of thioacetamide employed. Similarly, prolonging the time of treatment in order to increase the effectiveness of decay control obtainable with solutions much weaker than the herein recommended 4 to 5 per cent concentration, as is possible,:has definite practical limitations which ordinarily restrict the commercial applicability of this ex-- pedient rather narrowly. j i

Another thioamide of the fatty acid series. that has been found to give excellent decay control, especially against that due to penicillium molds, is thioformamide. When this compound is used, however, it should be of relatively high purity. Impurities such as free formic acid, commonly present in thioformamide prepared in the usual manner and not carefully purified, are apt to burn or otherwise injure the skin of lemons or other citrus fruit, for example, more or less severely. 'I'hiopropionamide, both alone and in mixture with propionamide, gives excellent mold control. Tests employing a 5% solution of such a mixture analyzing about 50% thiopropionamide haveiresulted very successfully both in respect of decay control and lack of injury to the fruit treated. Thiobutyramide and thiovaleramide, also their iso forms, are further compounds of this series which may be usefully employed in carrying out the new process.

Still higher members of the fatty acid series of thioamides can also be satisfactorily used, but since they aredifiicultly or not appreciably soluble in plain water, it is necessary as a practical matter to use a different'solvent in preparing treating solutions of them feasible to employ in commercial packing house operations. Although they aregenerally soluble in alcohol, and also act'eifectively in alcoholic solution, such solution's-would be ordinarily too expensive for commerciaf use. But they are also soluble as a rule in dilute water solutions ofcommon alkaline agents. Thus, solutions of these higher members of the series in water containing 0.5% caustic soda or 1% soda ash, for example, are entirely practical to employ commercially. Moreover the alkaline component of the solvent seems not only to be without adverse effect upon the decay-controlling power of these compounds but actually to increase it in at least some cases.

- The action of the thioamides in controlling decay appears to be actively fungicidal rather thanmerely inhibiting. Just why they act as theydo-on certain decay organisms has not yet been established. As a class, thioamides are known to be very active chemically, combining with both acids and alkalies to form well defined salts. There is accordingly some reason to think that, in acting upon those decay organisms against which they are effective, they may possibly diffuse through the cell walls of the spores and chemically combine with the protein of the spores. It is .to be understood, however, that the present invention is based upon observed facts, and is not dependent upon the correctness of However, it should be noted that, far from being universal'orindiscriminate in their fungicidal or decay-controlling action, the thioamides of the fatty acid series exhibit toward different rot organisms a definitely selective action that is quite unpredictable. Thus, while thioacetamide is very effective against the penicillium molds of citrus,

namely, P. digitatum, P. italicum and P. Tosca,

it is only weakly effective against the penicillium molds of apples. It is quite effective against brown rot of citrus, Phytopthom citropthom, but has little or no effect on cottony rot, Sclerotim'a libertiana, of lemons in storage. Again, while it is very effective against the alternaria rot, Alternaria citri, as well as against the two stem-end rots, Diplodia natalensz's and Phomopsis citrz', it

has been found that when large lots of citrus fruits are effectively treated with thioacetamide under commercial conditions for protection against these rots, there may nevertheless occur in those treated lots considerable development of Dothiorella, Botrytis rot, Botrytis cinerea, and sour rot Oospora citriaurantii. The reason for this selectivity in fungicidal action of the fatty acid thioamides is as yet wholly obscure, rendering it impossible, in the absence of actual trial, to predict what their action will be against a given specific rot organism. V

In contrast to the surprising discovery that thioamides as a class are highly effective in con trolling certain types of decay and yet, despite their well known chemical activity, are non-injurious to fruits and vegetables, it was found in the course of the research'which resulted in the foregoing discovery that most other types of compounds tried, which have a chemical structure more or less analogous to that of thiourea and which, it might therefore be thought, would therefore prove similarly useful for decay-control purposes, are infact quite useless for any such purpose, either because they possess little or no decay-controlling action, or because they act injuriously upon fresh fruits and vegetables, or for both reasons. Among compounds in this category are: thiosemicarbazide, diphenylthiourea, ethyldithiocarbamate, dithiocarbamic acid, phenothiazine and sodium thiocyanate, all of which give relatively poor decay control or none at all;v

also potassium ethyl xanthogenate and ethyl thiocarbamate, both of which give fair decay control but are injurious to the treated articles, severely burning the skin of citrus fruit, for example.

In commercially practicing the new process, use may be made of any of several well known types of apparatus installations heretofore commonly used especially in citrus fruit packing houses or plants, in treating the throughput with borax' solution, for example. In one such form, the decay control solution, which in this instance may be a 5% water solution of thioacetamide, is contained in a dip tank located immediately following the usual washer and plain water rinse through which the fruit is caused to travel in a continuous stream in the customary preliminary washing or cleansing operation. The washed fruit then enters and passes through the dip tank containing the thioacetamide solution, the tank being desirably provided with a submerger device of conventional type whereby to ensure thorough wetting of the entire surface of every fruit with the treating solution. As the stream of fruit, after such submergence, travels out of -'-the treating tank restingion the -usual elevator conveyor, it may be,heaviW-Siarayed-with treat- :Zing solution puni'pedifrom the tank. -Indeed,:instead ofusin'g-a 'dip'tank as described; application of the treating solution to the'washed fruit 1.

may be-wholly'by fiood sprays directed upon the stream of fruit'as it rests on a roller conveyor, for example, or as it is advanced on rotary brushes whichaidineifecting thorough application; In either mode'of application, it is found desirable to add to the treating solution a small proportion of 'a-surface tension depressant or conditioning agent, not to enhance impregnation of the fruit or vegetable rind or skin tissues w'ith the decay- -controlagent and thus improve decay control'for this is found not to result to any substantial extent with the; thioamides-but rather to favor rapid and uniform drainingoif oftheitrea'ting solution'from'the treated'articles, thereby minimizingthe amount of surfac'e'residu'e of excess decaycontrol agent'l'eft thereon, "especially if the fruit is'not rinsed with plain water after being treated. Rinsing with plain water after treatment is found to reduce somewhat the effectiveness of decay control, but may nevertheless be resorted to.

Another mode of applying the treating solution, and one which affords certain very important practical advantages, is to direct upon the traveling stream of previously washed fruit, a very fine spray (which may be virtually a fog or mist) of the treating solution, most desirably containing a small proportion of a surface tension depressant or conditioning agent. By maintaining constant the speed at which the stream of articles is caused to advance (e. g. on a roller conveyor which turns the articles over and over), and by supplying the treating solution to the fine-spraying or atomizing nozzles, under constant pressure and at constant concentration, it becomes possible to deposit upon each article substantially the same exactly predetermined small quantity of treating solution which, upon mixing with water still clinging to said article as a result of the preceding washing and rinsing, will provide a resultant quantity and concentration of decay-control agent on the article suitable to give adequate decay control. This result is more perfect- 1y achieved if the treating solution contains a suitable small percentage, say 0.05%, of surface conditioning agent. The surface tension of the resultant liquid mixture on the article surface, even though the concentration of said conditioning agent will be lowered to 0.025% in a typical case, will be so low that the mixture will film out uniformly and very thinly over the article surface, thereby causing rapid run-off of excess liquid and consequently greatly accelerated surface-drying of the article. At the same time, the exact amount of decay-control agent which the article will finally carry when ready for shipment to market can in this way be rather precisely predetermined and held down to the minimum sufficient to achieve a desired degree of decay control.

What is claimed is:

1. In the preparation of unpeeled whole fresh fruits and vegetables for market, the process of protecting them against fungoid decay spoilage which comprises applying to the skin thereof an aqueous solution of thioacetamide at a concentration of at least 1 per cent, the temperature of said solution being between 60 and 100 F. as approximate limits.

2. In the preparation of unpeeled whole fresh fruits and vegetables for market, the process of land 5 per cent.

protecting them: against fungoid decay spoilage which comprises applying to the skin thereof an 'aqueous medium containing thioacetamide at a concentration between-the approximate limits of 3. :In the preparation of unpeeled :whole'fresh fruits and vegetables-Tor market; "the process of protecting'them against fungoid de'cayspoilage which comprises'ap'p'lying to the skinthereof an :l 'and 5 per' cent, and-at a temperature between 60 'and'1100FF. 'as approximateilimits. I v.

14. In the preparation:cf unpeeled whole fresh fruits and vegetables for market, :the process'of protecting themagainst fungoid dec'ay s'poilage whichzcomprises applyingto the skin thereof an aqueous medium containing approximately 4 to 5 uper cent thioacetamide, at a temperature on the order-of 60 to 100 F. 3 I M i 5. In the preparationof unp'ee l'ed whole'fresh "fruits and vegetables for :market; the f process of protecting them 'against'fungoid decay spoilage which comprises applying to the skin thereof an aqueous solution of thioformamide at decay-controlling concentration.

6. In the preparation of unpeeled whole fresh fruits and vegetables for market, the process of protecting them against fungoid decay spoilage which comprises applying to the skin thereof an aqueous solution of thiopropionamide at decaycontrolling concentration.

'7. In the preparation of unpeeled whole fresh fruits and vegetables for market, the process of protecting them against fungoid decay spoilage which comprises applying to the skin thereof an aqueous solution of thiopropionamide at decaycontrolling concentration, said solution also containing propionamide. v

8. In the preparation of unpeeled whole fresh citrus fruits and vegetables for market, the process of protecting them against fungoid decay spoilage which comprises applying to the skin thereof an aqueous medium containing at least 1 per cent of a fatty acid thioamide that is relatively insoluble in water alone, said medium containing a solubilizing agent.

9. In the preparation of unpeeled whole fresh citrus fruits and vegetables for market, the process of protecting them against fungoid decay spoilage Which comprises applying to the skin thereof an aqueous medium containing, at least 1 per cent of a fatty acid thioamide that is relatively insoluble in water alone, said medium containing an alkaline solubilizing agent.

10. In the preparation for market of unpeeled Whole citrus fruit that has been exposed to infection by fungoid rot organisms, the process which comprises protecting said fruit against fungoid decay spoilage by applying to the skin thereof a solution of an amide of a thioacid of the fatty acid series.

11. The process defined in claim 10, wherein said fruit has been exposed to infection by stemend rot.

12. In the preparation for market of unpeeled whole citrus fruit that has been exposed to infection by fungoid rot organisms, which comprises protecting said fruit against fungoid decay spoilage by applying to the skin thereof an aqeuous solution of thioacetamide.

13. The process defined in claim 12, wherein said fruit has been exposed to stem-end rot.

14. The process defined in claim 13, wherein the thioacetamide is employed at a concentration within the approximate range of from 1 to 5 percent.

15. In the preparation of unpeeled whole fresh citrus fruits and vegetables for, market, the process of protecting them against fungoid decay spoilage which comprises applying to the skin thereof an aqueous solution of a thioamide of the fatty acid series containingv a small proportion of a surface conditioning agent.

16. The process set forth in claim 15, wherein the articles to be treated are caused to move in a 12 fungus rot which comprises: applying to the skin of whole citrus fruit, melons and vegetables an aqueous medium containing between 1% and 5% of thioacetamide and a small amount of surfacetension depressant, said aqueous medium being at a temperature of between and F.

CHARLES D. COTHRAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,068,081 Sharma Jan. 19, 1937 Denny Sept. 21, 1937 OTHER REFERENCES Uses and Applications of Chemicals and Related Materials, vol. II, 1944, ed... by T. C. Gregory, page 2'75, published by Reinhold Publishing Corp., 330 W. 42nd Street, N. Y. 

1. IN THE PREPARATION OF UNPEELED WHOLE FRESH FRUITS AND VEGETABLES FOR MARKET, THE PROCESS OF PROTECTING THEM AGAINST FUNGOID DECAY SPOILAGE WHICH COMPRISES APPLYING TO THE SKIN THEREOF AN AQUEOUS SOLUTION OF THIOACETAMIDE AT A CONCENTRATION OF AT LEAST 1 PER CENT, THE TEMPERATURE OF SAID SOLUTION BEING BETWEEN 60* AND 100* F. AS APPROXIMATE LIMITS. 